lntraairway Thermal Profiles during Exercise and Hyperventilation in Normal Man. E. R. McFadden, Jr., and B. M. Pichurko. With the technical assistance of Brian ...
lntraairway Thermal Profiles during Exercise and Hyperventilation in Normal Man E. R. McFadden, Jr., and B. M. Pichurko
With the technical assistance of Brian Sullivan and Steven Pardee Shipley Institute of Medicine and the Departments of Medicine of the Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, and The Asthma and Allergic Disease Center and Departments of Medicine, University Hospitals and Case Western Reserve University School ofMedicine, Cleveland, Ohio 44106
Abstract When large volumes of air are inhaled at rapid rates of ventilation, substantial segments of the tracheobronchial tree become involved in the conditioning process and the inspirate does not reach body conditions of temperature and humidity until it passes well into the peripheral bronchi. To determine if the manner in which ventilation is elevated is an important factor in producing this response, we measured the temperature of the airstream at six points in the tracheobronchial tree from the pharynx to the subsegmental bronchi during 5 min of exercise and voluntary hyperventilation in seven normal subjects while they inhaled frigid air. Minute ventilation and respiratory frequency were recorded at minute intervals and intrathoracic temperatures were measured continuously. With both forms of hyperpnea, airway temperature fell dramatically, and there were no significant differences between exercise and hyperventilation. These results demonstrate that the thermal events that occur within the lung during short, moderately intense degrees of exercise can be readily simulated by voluntary hyperventilation when ventilation and inspired air conditions are matched. Our data also indicate that this form of exercise does not result in an increase in airstream temperature and raise the possibility that the bronchial blood supply may be determined by the local thermal needs of the airways to recover heat and water independent of, at least moderate, increases in cardiac output.
Introduction Data derived from direct measurements within the tracheobronchial tree demonstrate that when minute ventilation is voluntarily increased, the temperature of the airstream within the intrathoracic airways of normal subjects falls in a predictable fashion, and at the point at which the air reaches body conditions of temperature and humidity, moves deep into the periphery of the lung (1, 2). In these studies, the subjects voluntarily performed hyperventilation which resulted in very little metabolic or cardiac stress, and so it is not known if the findings are applicable to other situations, such as exercise, in which major increases in cardiac output and heat production regularly occur. To provide data on this point, as well as to gain more insight into the factors controlling the transfer of heat and water, we have recorded the Address correspondence to Dr. McFadden, Asthma and Allergic Disease Center, University Hospitals, Case Western Reserve University School of Medicine, 2074 Abington Rd., Cleveland, OH 44106. Receivedfor publication 22 January 1985 and in revisedform 6 May 1985. J. Clin. Invest. © The American Society for Clinical Investigation, Inc. 0021-9738/85/09/1007/04 $ 1.00 Volume 76, September 1985, 1007-1010
thermal profiles that develop within the intrathoracic airways in normal subjects during both forms of hyperpnea. Our observations form the basis of this report.
Methods Seven normal volunteers (five males and two females) with a mean age of 29±2 (SEM) yr served as our subjects. After informed consent was obtained, the nose and throat of each subject were anesthetized with 2% lidocaine and a fiberoptic bronchoscope was inserted through the nasopharynx into a subsegmental bronchus of the anterior segment of the right lower lobe. During the passage of the endoscope, the distances from the tip of the nose to the major anatomic landmarks were recorded. As in a previous study, a specially designed flexible thermal probe containing multiple small thermistors was inserted into a subsegmental bronchus (2). The distance from the nose to the proximal end of the probe was recorded and the bronchoscope was removed. The probe was withdrawn in small recorded increments until the most distal thermistor showed fluctuations in temperature with a deep breath, confirming its location in an unobstructed bronchus. By knowing the length of the probe, the distance the tip was inserted, and the location of each anatomic landmark relative to the tip of the nose, the position of each thermistor within the tracheobronchial tree could be determined. Minimal anesthesia was used in the airways during the positioning of the probe and, once the probe was inserted, it was well tolerated. No additional anesthesia was given or needed in any instance after the probe was in place. The stability of the position of the probe was continuously verified as in earlier experiments (2). The technical features of the probe have been reported previously (2). In brief, the thermistors were 250 ,lm in diameter, evenly spaced at 4.3 cm from each other, and arranged in a spiral pattern over the distal 30.2 cm of the probe. Each thermistor was electrically and physically isolated from its neighbor, and the output of each was sampled approximately 8 times per second with an analog to Digital converter and a PDP- I 1 computer (Digital Equipment Corp., Marlboro, MA). The 63% response time of the probe assembly was 0.25 s in stirred water. After the probe was secured in position, each subject performed 5 min of exhausting leg work on a cycle ergometer (mean workload = 1071±96 kilopondmeter) while inhaling frigid air through a heat exchanger (3-5). The water content of the inspired air was
